Do Aspens Turn in Clusters?

How much does Scooter Libby really know about trees?

In Sunday's New York Times, reporter Judith Miller described her testimony to the grand jury investigating the leaked identity of CIA operative Valerie Plame. Miller was quizzed about a cryptic letter she received from her confidential source, I. Lewis "Scooter" Libby. "You went into jail in the summer," wrote Libby. "It is fall now … Out West, where you vacation, the aspens will already be turning. They turn in clusters, because their roots connect them. Come back to work—and life." Do aspens really turn in clusters because their roots connect them?

No. Aspen trees do grow in clusters, or "clones," that share a common root system and have identical DNA. That doesn't mean they all "turn"—that is, change colors—at the same time, though. Leaves turn colors in the fall according to both genetic and environmental factors; the exact day depends on the sunlight, temperature, and precipitation to which they're exposed. Since aspen clusters can be quite expansive—the largest single organism on record contains more than 47,000 identical, interconnected "stems" spread out over more than 100 acres—certain trees could get more sunlight than others and change color on different schedules. * A week or more might elapse between the turning of the first and last trees in a stand of aspens.

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Shared genes do control some stages of the aspen life cycle. In the spring, for example, clusters of connected aspens all grow their leaves back at the same time. Different stems in the same clone also share physical traits, like bark color. When clusters of aspens turn in the fall, they all turn the same color: The leaves on every tree in one clone may turn gold, while those on the trees in another clone turn crimson.

Aspen clones develop through a process of asexual reproduction called "root suckering." Unlike many other trees, new aspens rarely come from seeds; they almost always grow as extensions from an existing root system. * Suckers can pop out of the ground in great numbers—tens of thousands per acre—and can appear dozens of feet away from the nearest stem. Each new sucker gets the benefit of a pre-existing root system that delivers nutrients from the soil. As each one matures, it sends out its own roots, which in turn produce more suckers. (Aspens aren't the only trees that propagate through root suckering. Varieties like the black locust, sassafras, beech, and white poplar can clone themselves in the same way.)

Explainer thanks Michael Grant of the University of Colorado at Boulder.

Correction, Oct. 18, 2005: This article originally stated that aspens don't deposit seeds. They do lay down seeds, but these offspring almost never reach maturity. Click here to return to the corrected sentence.

Correction, Nov. 29, 2005:This piece originally stated that the largest cluster of interconnected aspens on record spans 17 acres. It covers more than 100 acres. Click here to return to the corrected sentence.